Auction house Spink is set to break the $1million mark for a unique piece of philatelic history.

A 150-year-old Hong Kong stamp is set to be auctioned in Hong Kong on January 17. In 2011, the stamp was sold for a record $824k.

The 1865 96c. olive-bistre block of four is the only unused multiple of its kind in existence. Only forty eight unused examples of the stamp have been recorded.

Most important item

According to Spink this is the most important item of Hong Kong philately. No other block or cover, despite their rarity, can compare with this block. It is the one and only 96c. olive-bistre, the right margin block of four with full original gum, superb centring and exceptionally fresh colour.

The 96c. olive-bistre had a very short but sweet life story. They were released by the Post Office around January or February 1865 and were withdrawn when the correct brownish grey stamps arrived during late July or August 1865.

A Mistake that Became an Asset

Initially the Hong Kong Post Office failed to notice that this new supply of stamps was printed in an olive-bistre colour. There was no reason for this change and it is believed that it was simply a mistake on the part of De la Rue.

The fact that this stamp is not known overprinted «SPECIMEN» also indicates that it is a genuine error of colour. The mistake was discovered when the stamps were needed by the Post Office, but it was too late to prevent this incorrect colour being used.